The present invention relates generally to ultrasonic equipment and in particular to an ultrasound machine and method of operating the ultrasound machine to assess the underlying structure of collagen in tissue as may provide insight into cervical competence.
Abnormal cervical behavior contributes to both post-term and preterm pregnancy. With respect to the former, failed inductions of labor cause an increase in cesarean delivery, with longer hospitalizations and greater maternal/neonatal morbidity. Ultrasound prediction (measuring cervical length) and biochemical testing of cervical secretions do not effectively predict which patients at term will have successful inductions.
Preterm delivery is an even greater problem, resulting in significant infant mortality and morbidity (including long-term neurodisability) costing more than $26 billion annually in the US alone. Despite intense research, preterm birth rates have increased over the past century in part due to a lack of effective therapies in the face of a greater number of high-risk pregnancies. Drugs that reduce inflammation and/or inhibit uterine contractions do not prevent preterm birth, nor does cerclage (a suture around the cervix to tie it closed). Currently, ultrasound is used to measure cervical length in an effort to predict preterm delivery (associated with shortening). However, the American College of Obstetricians and Gynecologists cautions that the predictive value of this assessment is of uncertain significance because there are no therapies proven to prevent preterm birth.
The underlying cause of both post-term delivery and preterm delivery appears to be abnormal cervical remodeling (delayed in the first case, premature or accelerated in the second). Cervical remodeling occurs normally during pregnancy and results in a softening of cervical tissue before cervical shortening. The ability to accurately assess and study cervical remodeling (in an effort to understand normal versus abnormal changes) could provide improved prediction of preterm delivery, guide development of innovative therapeutic strategies, and permit monitoring of those pregnancies, as well as predict which patients will have successful inductions of labor.
Cervical shortening in the second trimester is often used to evaluate preterm birth risk because it is inversely related to preterm birth risk regardless of obstetrical history. Nevertheless, most women with a short cervix in the second trimester have successful term deliveries and, further, most nulliparous (first pregnancy) women who deliver preterm have normal second trimester cervical length. This underscores the limitation of this measure.
US Patent Application publication number 2010/0222679, filed Feb. 27, 2009, assigned to the assignee of the present invention and hereby incorporated by reference, describes a technique of assessing the underlying structure of collagen fibers in tissue, for example, in the cervix. This technique looks at normalized ultrasonic backscatter power at different angles in the plane aligned with or crossing the cervical axis. Generally an increase in backscatter loss as a function of angle (compared to the backscatter provided by a phantom with spherical scatters) indicates an increase in organization of that tissue, for example a greater number of aligned collagen fibers.
This analysis of underlying tissue structure (e.g. collagen fiber organization), in addition to or instead of macroscopic tissue properties such as elasticity, presented a new approach and technique for evaluating collagenous tissue such as that of the cervix and thus for the evaluation of cervical competence.